Airborne maritime surveillance platforms employ low band radars that operate at UHF frequencies. Other low band surveillance radars have been designed to use S-Band or L-band. Typical platforms use radar with an approximately 50 MHz operational bandwidth. If a 50 MHZ radar platform is used, the instantaneous pulse bandwidth is insufficient to achieve 1 m resolution in down-range. Generally, a resolution of at least 1 m is required to carry out robust image exploitation of incoming targets. The required resolution can be obtained in cross-range with a bistatic radar imaging system that uses a precise oscillator to maintain coherence between the transmitting and receiving platforms.
There are other advantages to bistatic inverse synthetic aperture radar (ISAR) imaging. Tracking of the target from two (or more) platforms can be combined to arrive at a more accurate kinematic profile (e.g., position, speed, heading) of the target. There is reason to believe that bistatic sea clutter may be less “spiky” than the equivalent monostatic sea clutter, and hence that bistatic geometries are more favorable for the detection of small targets. Also, multipath mitigation may be more easily realizable with a bistatic imaging system due to higher decorrelation of the multipath return in the radar compared to the monostatic scenario. In addition, the spatial diversity afforded by bistatic/multistatic systems allows for different aspects of a target to be viewed simultaneously. Also, it may be increasingly difficult to successfully focus jamming on multiple receivers in a bistatic/multistatic system compared to a single receiver.
However, unlike the typical scenario in SAR imaging, airborne ISAR imaging is more complicated because both the platform and the target are moving during the course of the data collection dwell. Conventional ISAR imaging techniques often produce images with unwanted distortion.